1. Field of the Invention
This invention relates generally to power steering load compensation systems and, more particularly, to an apparatus which uses a power steering pressure sensor to monitor the output of a power steering pump in order to provide pressure information to an engine controller so that the idle speed of the engine may be adjusted in accordance with the output of the power steering pump, thereby minimizing variations in idle speed based upon operation of the power steering system.
2. Description of the Related Art
The use of hydraulically assisted power steering in medium and larger sized automobiles has become generally standard throughout the automotive industry. Most vehicle operators enjoy the ease of use which a power steering system provides. In operation, power steering systems typically use a power rack-and-pinion system or an integral power steering gear assembly. Rack-and-pinion systems are typically installed on front wheel drive cars, while integral power steering gear systems are used on rear-wheel drive vehicles.
In a typical power steering system, the engine drives the power steering pump through a belt and pulley arrangement. The power steering pump includes a pressure hose and a return line, and typically also includes a control valve to modulate fluid pressure within the hydraulic circuit. The power steering pump generates fluid pressure. When the operator turns the steering wheel, the fluid pressure is directed to mechanically assist displacement of the steering assembly.
Although present power steering systems provide suitable assistance to facilitate the steering operation of the vehicle, at idle and low speeds, existing power steering systems exert a load on the engine which causes the idle speed to fluctuate in accordance with the load applied by the power steering pump. More specifically, with the vehicle at idle speed and the wheels generally centered, the power steering pump places minimal load on the engine, as no power steering pump assistance is required. When the operator displaces the steering wheel to the left or the right, hydraulic fluid pressure is used to displace the steered wheels. In order to provide sufficient hydraulic fluid pressure, the power steering pump places a load on the engine which causes the idle speed revolutions per minute (RPM) to decrease or dip. Conversely, when the operator displaces the steering wheel to center the steered wheels, the power steering pump again places a load on the engine that causes the idle speed to drop. When the steered wheels are returned to the center position and the pressure output by the power steering pump drops, the power steering pump load on the engine decreases. A decrease in the power steering pump load consequently causes the engine idle speed to increase or surge. In addition to dips and surges, particularly during maneuvers in a parking lot, variations in the power steering pump load placed on the engine can cause vibrations due to vehicle body resonance when engine idle speed drops below the target idle speed.
Thus, it is an object of the present invention to provide power steering load compensation for an internal combustion engine.
It is a further object of the present invention to reduce engine speed variation resulting from variations in the power steering pump load as a steering wheel is moved, particularly at idle and low speeds.
It is yet a further object of the present invention to reduce vehicle body vibrations by maintaining a substantially constant idle speed regardless of power steering pump load.
It is yet a further object of the present invention to improve overall vehicle responsiveness while executing steering maneuvers at idle and low speeds.